The present invention relates generally to input devices for personal computers. More specifically, the present invention relates to a trackball-type input device for use with a portable personal computer.
For user input, the conventional portable computer typically includes an alphanumeric keyboard and some type of pointing/selecting device. One type of pointing/selecting device commonly used with portable computers is a trackball-type device. This type of device generally includes a trackball for controlling the movement of a cursor on the display screen and one or more actuator switches for selecting items highlighted by the cursor.
For portable computers, the designs for trackball-type devices fall generally into one of two categories: External or integral. External designs provide a trackball/actuator assembly that is separately housed and which attaches to the portable computer housing via a cable or specially-designed hardware. An integral design includes a trackball and one or more actuator switches which are integral to the computer housing. Typically, the trackball and actuator(s) are placed in the middle of the computer housing below the "SPACE" key of the alphanumeric keyboard. Examples of integral designs include designs by Toshiba Electronics Corporation, by AST Research Corporation, and by Compaq Computer Corporation, among others.
Although external designs allow for maximum use of limited computer-housing space for the keyboard layout, integral designs are often preferred because they provide a portable computer that is completely self-contained and easy to transport (i.e., no disassembly and/or separate storage is required for the trackball/actuator assembly to transport the portable computer). However, as will be described below, integral designs bring to the forefront the conflict between performance criteria for trackball-type devices and the severe size/space limitations generally associated with a portable computer.
The computer industry has adopted certain performance criteria for various input devices including trackball-type devices for use in portable computers. Among them are that 1) the input device should be easily accessible or usable by both left- and right-handed users; 2) the user-operated components should be large enough so that a user can easily locate and operate them by "feel" (i.e., the user does not have to visually locate the components each time to operate them); 3) the pressure required to activate an actuator switch should be appropriate: not so much as to cause excess strain on the typical user, and not so little as to result in frequent accidental activation; and 4) the design should be durable enough so that the device can be operated frequently without failure over the useful life of the portable computer.
At odds with these criteria is the reality that there are severe size/space limitations associated with portable computers. Market forces place the industry under increasing pressure to provide more capability and peripherals in a more compact and lightweight case. Hence, computer housing space, both inside and out, is at a premium. Also, many portable computer manufacturers aspire to provide a keyboard layout which is comfortable for the typical user and which emulates the conventional multi-function keyboard layout commonly used with desktop computers. This last consideration, in combination with the first, severely limits the amount of surface area remaining to implement the desired trackball and actuator switch(es).
Most conventional integral designs deal with the foregoing conflict in a highly sub-optimal manner. For example, referring to FIG. 1, there is shown a conventional integral trackball/actuator assembly 10 for a portable computer. The conventional actuator switch 12 for a portable computer consist of a keyplate 14 placed above a microswitch 16. The keyplate 14 is attached to one end of a length of flexible material 18 whose other end is fixed to the underside of the top surface of the computer housing 20 by, for example, a thermoweld or coldweld 22. In this arrangement, the length of flexible material 18 acts as a lever arm for the keyplate 14 and shares the stress produced when the user presses the keyplate. Consequently, the durability of the actuator switch 12 is in part a function of the length of the flexible material 18: the longer the material, the more durable the actuator switch.
To produce thermoweld or coldweld 22, a separate step in the manufacturing process for the input device is typically required. This adds cost and time to the manufacturing process for the device. In addition, additional surface area is required to produce a welding joint that is substantial enough to withstand frequent activation by a user.
To provide good performance, the conventional actuator switch should include a) a keyplate which is large enough to enable the user to locate it by "feel", and b) a length of flexible material, and a thermoweld joint which are sufficient to provide the desired durability. It should now be appreciated that implementing each of these features requires a considerable amount of surface area. However, in view of the size and space considerations outlined above, the required surface area is often not available. Consequently, compromises in the size of the keyplate 14, the length of the flexible material 18, and/or the size of the thermoweld joint are often made resulting in degraded performance. What is needed, therefore, is a trackball/actuator design which provides good performance in a very small space.